First draft of the Y2038 design document

[Joseph Myers]

On Mon, 26 Oct 2015, Rich Felker wrote:

> While _FILE_OFFSET_BITS or _TIME_BITS avoids an ABI transition in
> libc, they force an ABI transition for all third-party libraries that
> use the types. A library that uses off_t in its API and that's built
> with _FILE_OFFSET_BITS=64 is ABI-incompatible with a version of
> itself, or an application, built with _FILE_OFFSET_BITS=32. Thankfully

And Paul Eggert's analysis suggested that this ABI transition has largely 
happened - that affected libraries on GNU/Linux systems generally are 
built with _FILE_OFFSET_BITS=64 now.

> Another goal that might make this less distasteful than
> _FILE_OFFSET_BITS would be a planned timeline for switching the
> default to 64.

We need to get the fts patch reviewed.  At some point I might look at 
fixing bug 14106 (with new __*64 exports for all affected functions in any 
supported ISO C / POSIX standard) if noone else gets there first.  Then, 
given Paul Eggert's analysis, we could seriously look at changing the 
_FILE_OFFSET_BITS default (cf 
<https://sourceware.org/ml/libc-alpha/2014-03/msg00290.html> as a patch 
for that purpose - using _FILE_OFFSET_BITS=64 while building glibc itself 
would be hard, and no doubt the same would apply for _TIME_BITS=64).

I think for _TIME_BITS we'd similarly need to wait for widespread use 
before changing the default.

-- 
Joseph S. Myers
joseph@codesourcery.com